As the title says. Here's an image:
This is not my reputation.
It's the sum of your reputation on all SE sites. If you would like to check your profile for that, click on the "Accounts" tab to see the numbers. You are registered on 12 SE sites, and you got 100 on each site for connecting the accounts.
As Stefan already stated it is the sum of your reputation of all SE sites. Note that you have a general chat account which is not just for the TeX chat room, but for all SE chat rooms. However, your main site account (which is TeX.SE for you) is registered there as parent account. Because the chat account is for all sites, the total sum of all accounts is shown.